Henry Spencer wrote:
HS> Which still isn't anywhere near good enough toHS> power a climber, not when the power has to beHS> transmitted tens of thousands of kilometers through
Buckytubes (also known as single wall carbon
nanotubes.) have three kinds of crystallographic
lattice: armchair, zigzag, and chiral. Drawing:

http://www.islandone.org/LEOBiblio/buckytubes.jpg
Armchair buckytubes are ballistic conductors,
which means that their electric resistance is
relatively small (6500 Ohms) and independent
of length. If the armchair buckytubes are free
of defects, one millimeter long buckytube has
the same electric resistance as a buckytube
that is one thousand kilometers long. Toroidal
(or closed loop) buckytube would have no
contacts, so its resistance would be extremely
small. (Nobody knows how small.) The maximum
current density of the armchair buckytubes is
about one billion amperes per square centimeter
-- 3 orders of magnitude more than the maximum
current density of copper! Zigzag and chiral
buckytubes behave like semiconductors.
I believe that armchair buckytubes could be used
above the ionosphere and power the climbers --
high tension wires in North America transport
electricity over hundreds of kilometers. Solar
flares are a nuisance because they generate
strong voltages in the conductive skyhook. I
believe that dividing the skyhook into segments
interspersed with line choke coils would solve
this problem. Note that the armchair buckytubes
are perfect wires for the coils.
If the skyhook is laid on the ground on the
magnetic equator and strong electric current
flows through it, the Earth magnetic field
generates Lorentz force which levitates the
cable. This is easier way to lift it into orbit
than using the rocket launchers.
Although skyhook is theoretically possible, it
makes no economic sense because it is vulnerable
to terrorists and more expensive than related
technologies: orbital slings and geomagnetic
levitation. Orbital slings can be made now from
relatively cheap, commercially available fibers.
(By the way, I made a new thread in sci.space.tech
named 'Levitating geomagnetic buckytubes.')

I don't see why this has to be the case for a "beanstalk" if located
in a isolated equatorial island. Any plane or boat coming anywhere
near it could be detected and intercepted from hundreds of miles away.
Bob Clark

Beanstalk was not mentioned in the holy Quran, so it is
a kafir idea and it must be destroyed to save the world.
We are going to mail our time bomb up the beanstalk so
that it breaks it into two parts: the bottom part will
plunge into the atmosphere, while the upper part will
be hurled beyond the gravity of the earth.
Islamic Beanstalk Busters
La illaha illallah Muhammadum rasullullah!

Granted, you technically can say what you will (related to Mat. Sci.) on
this news group. However, can you please try to respond to discussions
with some small bit of respect/inteligence?
Seth
p.s.
If you do as recommended by me, I'm sure that some lengthy, scientific
and productive discussion (right or wrong on anyone's part) will ensue.

Rotators strike me as a better idea than beanstalks. However,
they may not be the best case for my pulley idea. Unlike a
beanstalk which is lifting small masses up and down in the
fashion of a continuous pipeline, rotators need to catch and
throw fairly large masses at a time, with consequent big changes
in tether tension. I'm not sure that pulleys are right for this
regime. Furthermore, rotators can be used without much
"elevating" at all. Catch at one angular position, release at
another. Fine tune by shifting mass near the "hub". No need
to shift mass near the tips.

One of the great stupid things to do that I have seen recently is to
talk about nanotubes with cross posting to a lot of different newsgroups.
The real smarts and the pseudo-smarts get into wars with each other.
To a large extent, the information content of the messages is dwarfed by
the emotional content.
Really dumb thing to do, but then there are people who enjoy the flurry
of semi-intellectual activity.
I will read about a dozen more elements of this thread and evaluate the
usefulness of the time consumed in reading it.
Enjoy yourselves, as evidently does seem to happen.
sci.space.policy ...... ?????

Welcome to the real world where a single invention/product can affect a
number of people doing totally diffirent things. As it was I had trimmed out
a number of newsgroups before I posted. It is my understanding that posting
to more than three groups at a time is getting carried away.
Sci.Astro - Where the discussion started as far as I can tell.
Sci.Space.Policy - Where the discussion is make better rockets or can they be
replaced with a beanstalk.
Sci.materials - What is the real state of the art in Nanotubes.
Earl Colby Pottinger

--
I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos,
SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to

I think you show bad taste, nevertheless.
However, at least people who want to endlessly discuss this subject in
the sense of a disconnected semi-shouting match have kindly been
provided this opportunity for endless discussion over a whole bunch of
newsgroups.
This may be the real world, to use your phrase, but this "discussion"
actually will have almost no significance to any of the participants.

bulk
will
And yet the ignition of single flash bulb could ignite an entire structure?
I think you are putting too much faith in a single technology. We need the
stars, but in our eyes is the wrong place for achieving them.
David A. Smith

No, it will not. That bright flash needs oxygen to get the burning going.
You will not find oxygen available in either space or inside the resin bond
fibers together - no to mention the resin will act like a heat sink
preventing the rise in the nanotubes temperture. Check again, you claim only
applies to single uncoated tubes under a very bright light.
Earl Colby Pottinger

--
I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos,
SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to

of
needed
structure?
the
going.
bond
only
This is what is documented, yes. And was totally unexpected.
Lightning strikes near the "cable", will induce sympathetic current in the
cable. The heating can delaminate your cable, delamination in an area that
is in full atmosphere.
Note that the coating you mention will act as an insulator, retaining the
heat, so that a second "event", soon enough, will get it even hotter.
The highest loading should be outside the atmosphere, but it will be
non-zero in the atmopshere. It wouldn't do to go drifting off... but then
we are not talking about shadow square wire, are we?
David A. Smith

The length of cable within the atmosphere -- especially within the region
where lightning is an issue -- is such a small fraction of the total cable
length that all kinds of special precautions can be taken there without
increasing cable mass significantly.

the
that
cable
Sprites have been seen to 60 miles in altitude, and that is without a
"lightning rod". Other than not having any one carbon fiber contacting any
other, there isn't much you *can* do. Then there goes your strength.
David A. Smith

There's lots you can do. Failing all else, you can probably just switch
to Kevlar for the bottom 100km. It's only carrying its own weight, plus
dynamic loads and cable tension -- it doesn't *need* that much strength.

Possibly, depending on how conductive our hypothetical nanotube-based
material is. (It might not be very conductive; a good composite doesn't
have the fibers themselves in contact with each other much.) I would hope
it wouldn't have to be several meters every kilometer, because that might
add quite noticeably to the cable mass. In general, doing *something* to
the cable at intervals isn't a problem, provided the intervals are wide
and the something isn't too massive.

For what? Assuming a conducting cable, what circuit will the current
take?
And remember that although individual carbon nanotubes of some types are
good conductors, they are not necessarily in good electrical contact.
The elevator will not be a very good conductor, it's resistance over
significant distances will be quite high.

Making the bottom 100 miles out of kevlar, or whatever is not a big
problem.
The only reason that nanofiber materials are needed is the huge taper
implied if you tried to use conventional ones.
For example, making the bottom 100 miles out of kevlar would only
(about) double the total mass.
If you tried to do it along the whole length, you'r looking at billions of
times.

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